I'm looking online at different items to buy and am not sure if I can use powdered food colour as you would petal dust. They kind of have it lumped in the same category, so I'm not quite sure. The products categorised as 'dust colour' are a bit more expensive, so any help would be appreciated!

I'm looking at Barco powdered colour versus SK Professional. I want them mostly for dusting some color onto gumpaste flowers, etc.

Not familiar w/the brands you mention (Barco/SKPro) I can't say for sure but generally here in the US there is a world of difference between powdered colors and dusts.
Powdereds are lumpy, thicker(?), and far more intense in color than dusts which are softer both in color and compasistion(sp?). Can't think of the right words to discribe the differences.

You can use the powdered colour to dust your gumpaste flowers. To soften the colour mix it with a bit of cornstarch.

Excellent - thanks for the replies! I'll order them and give it a go

Crystal colors are a powder color that can be used to color icings, fondant and gumpaste as well as be used to dust things and be mixed with alcohols to paint with. So there are some out there that can be. I'm not sure about the brand you are looking at though.